1. Field of the Invention
The present invention relates to an optical switch device.
2. Description of the Related Art
In recent years, optical communication channel capacities have been urgently required to be increased along with an increase in the traffic on the Internet. An approach to the increase in a communication channel capacity is to increase a bit rate or adopt wavelength division multiplexing (WDM). Realization of the optical devices constituting such a system has been awaited.
WDM is a technique for transmitting numerous signals, which have different wavelengths, over one optical fiber, and increasing the data-carrying capacity of the optical fiber by carrying information at each wavelength. Almost all WDM systems employ an optical switch, in order to perform port switching in a redundant construction or to perform port switching for monitoring purposes, etc.
Moreover, when optical signals are transmitted over an optical fiber, a propagation loss differs from signal to signal, that is, from wavelength to wavelength. After the optical signals are transmitted over a long distance, the signal levels become different from wavelength to wavelength. This phenomenon becomes more obvious in a case where a branching device or an erbium-doped fiber (EDF) amplifier is disposed on a transmission line.
To this end, before optical signals are transmitted or received, the levels of the signals having different wavelengths must be made equal. As a solution, variable attenuator devices that control the level of individual wavelengths and optical switches are used to control optical output to be transmitted or received so that intensity of the optical output will be made equal for every wavelength.
Assuming that WDM is adopted, an optical signal level must be controlled for each wavelength (channel). Therefore, attenuators and optical switches that can vary an optical signal level for individual channels must be disposed. At present, individual devices are incorporated in a system, and the system is therefore large in size and expensive. In efforts to design the system compactly, a technique employing a waveguide (planar lightwave circuit (PLC)) has been developed but it is unsatisfactory in terms of cost and size.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 5-113582 (FIG. 3(a))
Patent Document 2: Japanese Patent No. 3008964
Patent Document 3: Japanese Unexamined Patent Application Publication No. 5-204000